1. Field of the Invention
The present invention relates to a multi-optical-path photoelectric safety apparatus having a light emitting unit and a light receiving unit. More particularly, the present invention relates to a multi-optical-path photoelectric safety apparatus comprising a floating blanking function.
2. Discussion of the Related Art
A multi-optical-path photoelectric safety apparatus is provided to ensure worker safety when using an apparatus involving a source of danger, such as a pressing machine or a folding machine. The multi-optical-path photoelectric safety apparatus comprises a light emitting unit and a light receiving unit. The light emitting unit comprises a large number of light emitting elements arranged in a row. The light receiving unit comprises a corresponding number of light receiving elements as the number of the light emitting elements, and they are also arranged in a row. The light emitting and receiving units form a protective barrier by making a light curtain. When a light blocking substance through which light cannot transmit enters a detection area of the protective barrier, the operation of a machine, such as a pressing machine, a folding machine, etc., is forcibly stopped.
When using a metalworking machine such as a folding machine, the worker may hold a part of a workpiece while working. In order to deal with the worker holding the workpiece, the multi-optical-path photoelectric safety apparatus comprises a floating blanking function.
The usual protection function of the multi-optical-path photoelectric safety apparatus is to forcibly stop the machine immediately when a light block state occurs regardless of the number of blocked optical paths. However, with the floating blanking function, the machine is not forcibly stopped until two contiguous (or adjacent) optical paths are blocked.
A related art device showing a floating blanking function will be discussed with reference to FIG. 8. In FIG. 8, a multi-optical-path photoelectric safety apparatus comprises a light emitting-receiving unit 1. A worker O stands in a safety area outside the light emitting-receiving unit 1 and from this area, the worker O inserts a workpiece W into a working apparatus 2 containing a source of danger and performs an operation, such as, bending of the workpiece W.
In the case where the workpiece W is simply inserted into the working apparatus 2, the workpiece W only blocks one optical path of a light curtain formed by the light emitting-receiving unit 1. Thus with the floating blanking function, the light emitting-receiving unit does not determine that a human body has entered, and this allows the working machine 2 to operate continuously.
However, if the worker is pulled into the working apparatus 2 along with the workpiece W and two contiguous (adjacent) optical paths become blocked, the operation of the working apparatus 2 is immediately stopped.
The floating blanking function is set for the entire detection area of the light curtain in the related art device.
However, if the floating blanking function serves the entire detection area of the light curtain, the distance between the light curtain and the apparatus protected by the light curtain, namely, the safety distance, needs to be increased and this causes a problem.
For example, if the size of the minimum detection body when the normal protection function operates is 25 mm in diameter, the size of the minimum detection body when the floating blanking function operates becomes 45 mm in diameter. Assuming that the response time of the light curtain and the time until the apparatus protected by the light curtain stops are 35 ms in total, the safety distance based on European Standard EN999 is 158 mm when the normal protection function operates. However, the safety distance becomes 906 mm when the floating blanking function operates.
Thus, for a pressing machine, a workpiece folding machine, etc., where the floating blanking function needs to be used, the machine and the light curtain installed ahead the machine need to be located 158 mm away from each other (the safety distance when using the normal protection function) plus 748 mm. Therefore, the distance x0 between the danger source 2 and the light curtain needs to be 906 mm. This means that the worker must stand working at a distant position away from the pressing machine or the workpiece folding machine.
Accordingly, since the worker must work at a distance away from the working machine, the distance the worker must move the workpiece to insert the workpiece into the working machine is also increased. Thus, this increased distance easily reduces the productivity of the machine.